1. Field of the Invention
The present invention relates to an electron emission device, and in particular, to an electron emission device which has driving electrodes with improved shape at the cross regions thereof to lower capacitance value and to minimize (or reduce or prevent) signal delay.
2. Description of Related Art
Depending upon the kinds of electron sources, electron emission devices can be classified into those using hot cathodes, or those using cold cathodes.
Among the electron emission devices using the cold cathodes, there are a field emitter array (FEA) type, a surface conduction emission (SCE) type, a metal-insulator-metal (MIM) type, and a metal-insulator-semiconductor (MIS) type.
An FEA-type electron emission device includes first and second substrates for forming a vacuum chamber (or a vacuum vessel). Electron emission regions are formed on the first substrate together with cathode and gate electrodes as the driving electrodes for controlling the emission of electrons from the electron emission regions. Phosphor layers are formed on a surface of the second substrate facing the first substrate together with an anode electrode for placing the phosphor layers in a high potential state.
The cathode and gate electrodes cross over each other while interposing an insulating layer therebetween, and opening portions are formed at the gate electrodes and the insulating layer to correspond to the respective cross regions of the gate and the cathode electrodes. Electron emission regions are formed on the cathode electrodes within the opening portions.
A scanning signal voltage is applied to a cathode electrode (or a gate electrode), and a data signal voltage is applied to the other electrode (e.g., the gate electrode if the scanning signal voltage is applied to the cathode electrode or the cathode electrode if the scanning signal voltage is applied to the gate electrode). Electric fields are formed around the electron emission regions at pixels where the voltage difference between the cathode and gate electrodes exceeds a threshold value, and electrons are emitted from those electron emission regions. The emitted electrons are attracted by the high voltage applied to the anode electrode, and collide against the corresponding phosphor layers to emit light.
In operation, a signal distortion may be made at the electron emission device. The driving signals may be delayed due to the resistance of the driving electrodes and the parasitic capacitance between the driving electrodes. The signal delay is proportional to the resistance and the capacitance. The capacitance is directly proportional to the dielectric constant of the insulating layer and the dimension of the overlapped regions of the cathode and gate electrodes, but is inversely proportional to the thickness of the insulating layer.
In this connection, it has been conventionally proposed that subsidiary electrodes should be formed on the driving electrodes with a high conductive metallic material to reduce the resistance, and the insulating layer should be made to reduce the capacitance, that is, formed with a new insulating material having a low dielectric constant or with a large thickness.
However, the formation of the new insulating material for reducing the capacitance to minimize (or reduce or prevent) the signal delay involves a high material cost and repeated experiments to develop a new material, and hence, is not suitable for mass production.
Furthermore, especially with respect to the technique of increasing the thickness of the insulating layer to reduce the capacitance, when the insulating layer is wet-etched to form opening portions, inclined sides are formed at the opening portions due to the isotropic effect of the wet etching process so that the opening portions of the gate electrodes are enlarged in size. In this case, the distance between the electron emission regions and the gate electrodes is increased to thereby increase the corresponding driving voltages so that it becomes difficult to fabricate a high resolution display device. In addition, the uniformity in the emission of electrons for the pixels is deteriorated.